WASHINGTON — Republicans seized her microphone. And gave her a megaphone.

Silenced on the Senate floor for condemning a peer, Senator Elizabeth Warren, Democrat of Massachusetts, emerged on Wednesday in a coveted role: the avatar of liberal resistance in the age of President Trump.

Instantly, the decision — led by Senator Mitch McConnell, the majority leader, who invoked a rarely enforced rule prohibiting senators from impugning the motives and conduct of a peer — amplified Ms. Warren’s message and further inflamed the angry Senate debate over Mr. Sessions’ nomination. He was confirmed on Wednesday.

For Ms. Warren’s supporters, it was the latest and most visceral example of a woman muzzled by men who seemed unwilling to listen.

“A lot of that’s about 2020 politics,” Senator John Thune, Republican of South Dakota, grumbled on MSNBC.

Mr. McConnell’s subsequent explanation for his maneuver seemed destined for a future Warren campaign ad: “She was warned. She was given an explanation. Nevertheless, she persisted.” After an unsuccessful effort to draft her for the 2016 presidential race, Ms. Warren is considered a very early front-runner for 2020, should she run.

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Mr. McConnell’s coda has already been repurposed as a sort of rallying cry. Across social media, Ms. Warren’s allies and supporters posted with the hashtag #shepersisted, calling to mind some Democrats’ embrace of the term “nasty woman” after Mr. Trump deployed it to describe Hillary Clinton during a debate. Appearing with Mrs. Clinton in New Hampshire in October, Ms. Warren reminded Mr. Trump that “nasty women vote.”

After the vote to bar Ms. Warren from speaking further about Mr. Sessions, other senators, including Bernie Sanders of Vermont and Tom Udall of New Mexico, read Mrs. King’s letter without facing any objection, prompting some activists to raise charges of sexism.

Ms. Warren has long displayed an instinct for capitalizing on highly visible fights. After she was barred from speaking on the Senate floor, she began reading the 1986 letter from Mrs. King on Facebook. By Wednesday evening, the video had attracted more than nine million views.

In the letter, Mrs. King, the widow of the Rev. Martin Luther King Jr., took aim at Mr. Sessions’s record on civil rights as a United States attorney in Alabama, saying he had used “the awesome power of his office to chill the free exercise of the vote by black citizens.” She called on the Senate not to confirm Mr. Sessions to a federal judgeship, and his nomination to that post was ultimately rejected.

On Wednesday morning, in a conference room in the Capitol — the vote prohibited Ms. Warren from speaking about the nomination only from the Senate floor — Ms. Warren addressed civil rights leaders, recounting her long night.

“What hit me the hardest was, it is about silence,” she said. “It’s about trying to shut people up. It’s about saying, ‘No, no, no, just go ahead and vote.’”

She went on.

“This is going to be hard,” she said. “We don’t have the tools. There’s going to be a lot that we will lose. But I guarantee, the one thing we will not lose, we will not lose our voices.”

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Spicer Responds to King Letter on Sessions

Asked about a letter that Coretta Scott King wrote regarding Jeff Sessions in 1986, the White House press secretary said he “would respectfully disagree with her assessment of Senator Sessions then and now.”

By THE NEW YORK TIMES on Publish Date February 8, 2017.
Photo by Mark Wilson/Getty Images.
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As Democrats strain to navigate the early days of the Trump presidency, weighing the merits of the blanket opposition that many in their base seem to crave, the latest rancor appeared to raise the likelihood of further confrontation in the Senate chamber.

Some left-leaning groups seemed comfortable with that.

“What the public needs to see from Democrats right now is more backbone and more standing on principle,” said Adam Green, a co-founder of the Progressive Change Campaign Committee. “Elizabeth Warren continues to be the model for good behavior.”

The timing is fortunate for Ms. Warren, whose fiery denunciations of corporate greed have long made her a Democratic celebrity.

Her new book deal was announced this week. Its title: “This Fight Is Our Fight: The Battle to Save America’s Middle Class.” Shortly after Mr. McConnell’s objection on Tuesday, Ms. Warren called a favorite TV anchor, MSNBC’s Rachel Maddow, and spoke live on the air.

On Wednesday, Republicans betrayed no regret for their move, accusing Ms. Warren of ignoring repeated warnings to avoid violating the Senate rule, known as Rule XIX. She had also read a letter from Edward M. Kennedy, who represented Massachusetts in the Senate, disparaging Mr. Sessions.

“You don’t insult — whether it be from a letter, or from a message from God, or on golden tablets,” said Senator John McCain of Arizona. “That’s the rules of the Senate. They want to complain about it, complain about it.”

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“If Mr. McConnell or anybody else wants to deny me the right to debate Jeff Sessions’s qualifications, go for it,” Mr. Sanders said from the Senate floor hours before the vote.

Since the election, Mr. Sanders and Ms. Warren have been among the lawmakers jockeying to be leading messengers for Democratic politics under the Trump administration.

There have been bumps. Last month, Ms. Warren faced rare criticism from liberals after voting in a Senate committee to approve Ben Carson as Mr. Trump’s secretary of housing and urban development, infuriating voters who had hoped for uniform opposition to Mr. Trump’s cabinet.

Defending herself on Facebook at the time, Ms. Warren wrote that she appreciated the feedback. “Unlike the new administration,” she said, “I don’t believe in ignoring or silencing people who disagree with the choices I make or the votes I take.”

This week, it seemed, all had been forgiven. MoveOn.org, the liberal political group, said it had collected about $300,000 in contributions for Ms. Warren since Tuesday night.

And by midafternoon, a fund-raising email from Ms. Warren had arrived in the inboxes of her supporters.

“I’m still banned from speaking on the Senate floor — but there’s still time for you to make your voice heard,” the email read, with a link to a page for contributions.

A version of this article appears in print on February 9, 2017, on Page A17 of the New York edition with the headline: Silencing Warren, G.O.P. Amplifies Her Message. Order Reprints|Today's Paper|Subscribe